A known drive control apparatus for a hybrid vehicle where wheels are driven by an engine and an electric motor is disclosed in JP2008-55993A (which will be hereinafter referred to as Reference 1), for example. In the hybrid vehicle (the vehicle) disclosed in Reference 1, the engine, the electric motor, and a transmission are connected to one another in series so that the vehicle is driven by a combination of the engine and the electric motor. According to the drive control apparatus disclosed in Reference 1, in a case where the vehicle is started from a stopped state, the wheels are driven by the electric motor. In a case of accelerating the vehicle during a driving state of the vehicle, a clutch mechanism disposed between the engine and the electric motor is brought into an engagement state, i.e., the engine and the electric motor are connected to each other via the clutch mechanism, so that the driving of the wheels by the electric motor is assisted by the engine.
In addition, in a case of decelerating the vehicle by a brake operation during the driving state, a regenerative brake is initially obtained. Then, in a case where a further braking force is required, the clutch mechanism is brought into the engagement state to thereby obtain an engine brake. According to the drive control apparatus disclosed in Reference 1, the clutch mechanism is operated depending on the situation so as to connect or disconnect between the engine and the electric motor.
In a case where the clutch mechanism is operated so as to connect between the engine and the electric motor, an impact may occur at the vehicle depending on a rotation speed of each of the engine and the electric motor. For example, when the engine, of which the rotation speed is lower than that of the electric motor, is connected to the electric motor in a state where the wheels are driven only by the electric motor, a driver of the vehicle may feel like the vehicle is pulled rearward because of a rapid deceleration of the vehicle. At this time, according to the drive control apparatus disclosed in Reference 1, the clutch mechanism is brought into the engagement state when an absolute difference between the rotation speed of the electric motor and the rotation speed of the engine becomes equal to or smaller than a predetermined value. Therefore, the impact that occurs at the vehicle when the clutch mechanism is brought into the engagement state is reduced to some extent.
Nevertheless, according to Reference 1, the clutch mechanism is brought into the engagement state only on a basis of the absolute difference between the rotation speed of the electric motor and the rotation speed of the engine. Thus, the behavior of the vehicle that occurs due to the engagement of the clutch mechanism may differ from the intention of the vehicle driver at that time. That is, the vehicle driver may have from a large discomfort by feeling that the vehicle is pulled rearward because the engine having the lower rotation speed than that of the electric motor is connected to the electric motor in a case where the clutch mechanism is operated so as to accelerate the vehicle during the driving state.
On the other hand, the vehicle driver may also have the same discomfort by feeling that the vehicle is pushed forward because the engine at a high rotation state is connected to the electric motor in a case where the clutch mechanism is operated so as to decelerate the vehicle.
A need thus exists for a drive control apparatus for a vehicle and a method of controlling a drive apparatus for a vehicle which are not susceptible to the drawback mentioned above.